Data Structures

Namespace: OpenEHR.RM.DataStructures

openEHR uses a small set of generic container classes to carry an entry's clinical content. The choice between them is constrained by archetypes, not by the RM itself.

Structure types

Class	openEHR equivalent	Shape
ItemTree	ITEM_TREE	Recursive tree of named items — most common
ItemList	ITEM_LIST	Flat ordered list of Element (no nesting)
ItemTable	ITEM_TABLE	Table of rows, each a Cluster
ItemSingle	ITEM_SINGLE	Exactly one Element

ItemTree

The workhorse structure. Holds a flat or nested mix of Element and Cluster items.

var tree = new ItemTree
{
    Name  = new DvText("Tree"),
    Items = new List<Item>
    {
        new Element
        {
            Name            = new DvText("Systolic"),
            ArchetypeNodeId = "at0004",
            Value           = new DvQuantity { Magnitude = 120, Units = "mm[Hg]" }
        },
        new Element
        {
            Name            = new DvText("Diastolic"),
            ArchetypeNodeId = "at0005",
            Value           = new DvQuantity { Magnitude = 80, Units = "mm[Hg]" }
        }
    }
};

Cluster

A named group of Item objects within an ItemTree, allowing nested structure.

var bpCluster = new Cluster
{
    Name            = new DvText("Blood pressure reading"),
    ArchetypeNodeId = "at0006",
    Items           = new List<Item> { systolicElement, diastolicElement }
};

Element

The atomic leaf node. Each Element holds exactly one DataValue in its Value property.

var ageElement = new Element
{
    Name            = new DvText("Age"),
    ArchetypeNodeId = "at0007",
    Value           = new DvCount { Magnitude = 45 }
};

Property	Type	Description
Value	DataValue?	The clinical value (any DvXxx type)
NullFlavour	DvCodedText?	Reason value is absent (e.g. "unknown", "not asked")
NullReason	DvText?	Free-text reason for null value

Null flavours

When Value is null, NullFlavour must be set using the openEHR null-flavour vocabulary (terminology_id = "openehr"):

Code	Meaning
253	unknown
271	not applicable
272	masked
273	not asked

ItemList

A flat ordered list — useful for simple observation panels where no nesting is needed.

var medications = new ItemList
{
    Name  = new DvText("Medication list"),
    Items = new List<Element> { drugElement, doseElement, routeElement }
};